Piezoelectric device



June 1940. T. G. KlNSLE-Y PIEZOELECTRIC DEVICE Filed Sept. 9, 1938 2Sheets-Sheet 1 INVENTOR By TIG/(INSLEY I/QM' ATTORNEY June 4, 1940. T.G. KINSLEY PIEZOELECTRIC DEVICE 2 Sheets-Sheet 2 Filed Sept. 9, 1938ATTORNEY Patented June 4, 1940 UNITED STATES PATENT OFFICE PIEZOELECTRIODEVICE Application September 9, 1938, Serial No. 229,131

8 Claims.

This invention relates to piezoelectric relays.

An object of the invention is to provide simple and compact electricterminal apparatus for a piezoelectric relay unit comprising a pluralityof superposed plates of piezoelectric material.

Another object of the invention is to provide a universal type ofpiezoelectric relay actuating unit which may be available for variouspurposes and mountings without likelihood of damage to the fragilepiezoelectric plates or to their delicate leads.

According to this invention a plurality of piezoelectric plates havingtheir opposite faces suitably coated with conducting material toconstitute electrode faces are superposed in a stack. One end of a verythin foil tape is placed in contact with one of the outer conductingelectrode surfaces and the remainder of the tape is carried in foldsinto the alternate spaces between plates. A second similar tape isplaced in contact with the other outer conducting electrode surface andis folded into the spaces intermediate those occupied by the first tape.A pair of conducting clamping members insulated from each other are usedto clamp the entire assemblage and to serve as electrical terminals.

In .the drawings,

Fig. 1 illustrates a loosely stacked assemblage of four piezoelectricplates;

Fig. 2, a relay employing the assemblage of Fig. 1;

Fig. 3, a modified relay employing a different mounting structure;

Fig. 4, the component elements of a unit having piezoelectric platesclamped at two margins to utilize a warping action;

Fig. 5, the assembled operating unit of Fig. 4;

Fig. 6, the component elements of another modification of the relay unitof Fig. 2;

Fig. '7, the assembled operating unit of Fig. 6; and

Fig. 8, a modification of the structure of Fig. 7.

Referring to Fig. l, which shows the manner in which the piezoelectricplates and the conducting terminals are assembled, plates I, 2, 3 and 4of piezoelectric material may, for example, consist of Rochelle salt,the plates being cut perpendicular to the X axis of the virgin materialand at an angle of 4.5 degrees to the Y and Z axes for longitudinalextension and contraction. Each plate .is provided on its two oppositeprincipal faces with a conducting electrode 5 which may consist of athin metallic coil sheet or of a coating of colloidal graphite obtainedby spraying on a graphite suspension such as the well-known aquadag.Terminal element 6 consists of an extremely thin strip of metallic foilwhich is folded so as to engage the upper surfaces of plates I and 3 andthe lower surfaces of plates 2 and l. Another terminal strip '5 isfolded in similar manner to engage the lower surfaces of plates 4 and 3and the upper surfaces of plates 2 and i. The margins of the plates l,2, 3 and 4'; are free from conducting material and an insulating spacer$3 is interposed between the lower end portions of terminal strips 6 andi so that the terminal strips are completely insulated from each other.

The strips 6 and l are attached to the Rochelle salt plates and theplates are cemented together to form a solid slab. For this purposeclear Duco manufactured by the DuPont Company has been found suitable.In order to prevent dehydration of the plates of piezoelectric materialand maintain high surface resistance the edges, outer surfaces andspaces between connections may be painted with a water-proof insulatingmaterial such as Victron lacquer.

In operation the piezoelectric plates l and 2 are caused to extend atthe same time that plates 3 and 4 contract, thus making thecementedtogether assemblage iiex laterally according to the direction ofthe applied electromotive force. This requires that plates 1! and 2 berelatively reversed so that an electric field downwardly directedthrough plate I will cause a longitudinal change in the same directionas an upwardly directed field through plate 2. In like manner, plates 3and 4 are arranged to extend or contract together and in reverse mannerto plates 8 and 2. The elongation or shrinkage of a crystal slab of thisorientation is inversely proportional to the thickness for a givenvoltage. Accordingly, the two pairs of thin plates for the same appliedVoltage provide twice the amplitude of displacement obtainable from adevice of otherwise identical dimensions composed of only one pair ofelements each twice as thick. This feature of thin plates or laminationsof piezoelectric material may be carried as far as desirable by the useof a greater number of plates and is limited only by the thickness towhich the plates may be ground or machined.

The unit of Fig. 1 is shown assembled with its armature contacts in Fig.2. The terminal ends of the plates are clamped together by a pair ofclamping members 9 and it which also tightly clamp the terminals II and[2 respectively in contact with terminal strips 6 and l. The outerelectrodes or coatings 5 of conductive material may be overlaid asindicated at l3 by a conducting foil to assist in electricallyconnecting the graphite coating to the terminal. Insulating spacers I4and I5 may also provide a high degree of insulation between theterminals. A flexible U-shaped armature member It may be connected toclamping member 9 by screws and to the free end of the plates by anintegral clip ll which extends partly around the plates to constrain thearmature member to move with the plates. A thin sheet of dielectricmaterial between clip I! and the outer coatings 5 precludes shortcircuiting. Armature member I6 may carry a contact member I8 of whichonly the stem, is shown in Fig. 2, the contacting portion of the member[8 cooperating to close a local circuit upon engagement with a contact,not shown, on the contiguous face of a supporting element l9 which isfastened at one end to the clamping member 9 and is adjustably supportedat the end near contact It by a spring 26, the position of which isdetermined by the setting of an adjusting set screw 2! to determine thespacing between contacts in the open circuit position of the relayarmature. If desired, a second contact IB' may be arranged in parallelto contact l8 with a similar contact spacing adjusting device. It will,therefore, be apparent that upon application of an electromotive forceof suitable magnitude and polarity to terminals II and I2 the plateswill flex to cause armature [6 to carry contact [8 into engagement withthe stationary contact.

In a device of the kind disclosed in Fig. l, the plates were constructedfrom Rochelle salt as described with a length of about 3 inches, abreadth of about inch and a thickness of approximately .015 inch. With'75 volts applied a force of the order of 4 grams was exerted betweenthe contacts after operation of the relay.

Fig. 3 illustrates a modified form of mounting of the piezoelectric unitof Fig. 1. The assemblage of piezoelectric plates is provided withterminal connections as described in connection with Figs. 1 and 2 andis clamped between clamping members 22 which are attached to a verticalframe 23 mounted on an insulating base block 124 and serving to carryadjustable back contact member 25 and front contact member 26. Thecontact members are mounted in supports which are insulated from frame23 by the insulation sheets 27 and 28 respectively. A movable contactelement 29 mounted astride the free end of the piezoelectric plateassemblage is insulated therefrom by thin sheets of mica dielectric 3Gand is electrically connected by flexible lead 3! to binding post 32.Front contact 25 is electrically connected through screw 33 insulatedfrom the frame 23 with a. conductor 34 connected to a terminal mountedon the insulating base block 24. Back contact member 25 is connectedthrough its support, an insulated screw 35 and lead 36 to terminal 31.The input terminals 38 and 39 which correspond to terminals II and E2 ofFig. 2 are respectively connected to terminal members 40 and 4| mountedon the base block. The manner of operation of this device to alternatelyclose two different circuits on its front and back contacts in themanner of a polarized relay depending upon the polarity of the impressedelectromotive force will be apparent.

Fig. 4 shows a disassembled view and Fig. 5 an assembly view of amultiplate piezoelectric device having a construction somewhat similarto that of the device of Fig. 2 in so far as the arrangement of platesand electrical connections is concerned. The piezoelectric plates mayconsist of Rochelle salt cut perpendicular to the X axis and with theirmargins parallel to the Y and Z axes. The two upper plates may be soarranged that they tend to extend in a diagonal direction through thecorners l and m and at the same time to contract along the diagonal 0 nwhile the lower twoplates are arranged for the converse operation.Accordingly, the assemblage of plates cemented together as described inconnection with Fig. 2 will, upon application of an electric field,undergo a warping action such that if the edges Z 0 and Z n be heldfixed the corner m will be displaced in an upward or downward directionand contact 42 carried thereby will be moved into or out of engagementwith a stationary contact.

The piezoelectric plate assemblage 43 is provided with terminals in thesame manner as is the structure of the preceding figures. In order torigidly mount the device, two identical clamping members 44 and 45 areused. They may be molded of Bakelite or other suitable insulatingmolding material. Each is provided with a. recessed shoulder portion 46with an adjacent upstanding projection 58 to receive the piezoelectricplates. The clamping members may be fixed together by means of grommets41 which may be molded into the clamping members and in as-'- sembly ofthe device may be spun in well-known manner. Terminals 48 and 49 mayeach be provided with U-shaped tongues which contact respectively withthe peripheries of the two grommets to simplify electrical connections.

Rochelle salt crystals are very easily cracked or broken in clamping ifthe surfaces are not extremely true and fiat. It is therefore advisableto so proportion and dimension the clamping members 44 and 45 as toallow space for the crystal and some clearance. The extra space may thenbe filled with a cement which Will dry hard when given sufficientventilation. Each of the members 44 and 45 is provided with a series ofventilating apertures 50 to permit drying of the cement used to hold thepiezoelectric plates and the Bakelite unit rigidly together. The fillingof the space with cement increases the efficiency of the unit byeliminating any freedom which might otherwise exist at the clamped basedue to irregularities in the crystal unit or the mounting details.

It will be apparent that the assembled unit of Fig. 5 may be very simplyand inexpensively made and that it will be rugged and will affordconsiderable protection to the crystal elements against mechanicalinjury. It is, moreover, capable of 'mounting and use in a wide varietyof structures in which an old unit may be quickly replaced by a new unitwhenever necessary or desirable.

Figs. 6 and '7 illustrate a modified form of relay unit operating byvirtue of longitudinal or extensional displacements to cause lateralflexure in the manner of the structure of Figs. 1, 2 and 3. Themultiplate assemblage is held clamped and cemented between identicalmolded members 5| and 52. The grommets serve in this instance both asrivets and as electric terminals. It will be understood that the freeend of the piezoelectric plates may carry a contact as at 53 or acontact of the type illustrated in Fig. 3 may be provided. The unit ofFig. 7 is adapted to be used in a structure such as that of Fig. 3 andwhen provided with both front and back contacts may be employed to closeeither of two cir-' cuits as in the apparatus of Fig. 3.

Fig. 8 discloses a modification of the structure of Fig. 7 in which theterminal strips 54 and 55 are both brought out at the end of thepiezoelectric plate with sufiicient lateral separation to provide thenecessary insulation. The end tabs 55 may be cemented to theirrespective base members 51 in addition to being held by the grommets orthe grommets alone may be employed to hold them in position. It will beobvious that this structure may, like that of Fig. 7, be provided withone or two contacts and may be mounted in a structure similar to that ofFig. 3.

Various circuits for operating piezoelectric relays and for permittingelectric charges to be applied and withdrawn in order to determine theoperation and release periods are disclosed in W. P. Mason, applicationSerial No. 131,160, filed March 16, 1937, relating to Piezoelectricapparatus and circuits; W. P. Mason, application Serial No. 173,770,filed November 10, 1937, relating to Vibrating piezoelectric relays; andD. G. Blattner and L. Vieth application Serial No. 228,- 357, filedSeptember 3, 1938, relating to Delay type piezoelectric relays.

What is claimed is:

1. An electrostatic device comprising a fiat plate of piezoelectricmaterial, conductive surfaces applied to the opposite faces andinsulated from each other and a rigid casing holding a portion of theperiphery of the plate in fixed position, the remaining portion of theperiphery being free to flex, said casing comprising two similar rigidclamping members each having a spacing projection to form a recessbetween the members to receive the plate of piezoelectric material, theprojection on one member being interrupted for a portion of the lengthof the member and the projection on the other member occupying only thespace provided by the interruption of the projection on said one memberand terminals connected respectively to the conductive surfaces andmounted on the casing.

2. A device according to claim 1, characterized in this, that the fiatplate is rectangular and that the casing extends along and holds twoadjacent margins of the plate leaving the other two margins free toflex.

3. An assemblage of piezoelectric plates each having conductive surfacesassociated with their principal plate faces and said plates beingstacked with the conductive surfaces in juxtaposition, two fiat terminalstrips of coating foil each having folds to enter the spaces between theplates and make contact with the conducting surfaces, the folds of onestrip alternating with the folds of adhesive used to mount the plate, apiezoelectric plate positioned in the recess between the ,members andmeans fastening the clamping members together to tightly clamp thepiezoelectric plate in position.

5. In combination, a pair of identical pre- .1;

formed clamping members each having an upstanding projection extendingalong a portion only of its length whereby a recess is formed betweenthem, a plurality of piezoelectric elements fitting into the recess andhaving conductive surfaces, means for impressing an electric chargebetween the surfaces on the opposite principal faces of said elements,and means cooperating to rigidly hold the clamping members in engagementwith the piezoelectric elements.

6. An assemblage of fiat piezoelectric plates each having its twoopposite principal faces overlaid with a layer of conducting material,the plates being stacked with their respectively adjacent conductivesurfaces in juxtaposition, two fiat terminal strips of coating foil,each having folds to enter the space between the plates and make contactwith the conducting surfaces, the folds of one strip alternating withthe folds of the other with respect to the spaces which they occupy, apair of rigid clamping members each engaging the stack on one of itsopposite principal faces, the outer free end of one terminal stripextending partly along and attached to one clamping member to beprotected thereby and the outer free end of the other terminal stripsimilarly extending along and attached to the other clamping member.

7. The combination according to claim 6, characterized in this, that theextending free ends of the terminal strips are covered by therespectively adjacent clamping members.

8. The combination in accordance with claim 6, characterized in this,that the extending free ends of the terminal strips are electricallyconnected respectively to terminals mounted on the respectively adjacentassociated clamping members.

THOMAS G. KINSLEY.

